#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<math.h>
int main()
{
	int xa = 0;
	int ya = 0;
	int xb = 0;
	int yb = 0;
	float cd = 0;
	scanf("%d %d\n%d %d", &xa, &ya, &xb, &yb);
	cd = sqrt((xb - xa) * (xb - xa) + (yb - ya) * (yb - ya));
	printf("%.3f", cd);



	return 0;
}